2009 SFB Workshop Presentation: In Vitro Analysis of Novel Porous PEEK Orthopedic Biomaterial

    • Reference:
    • Tandy BC, VanGordon S, Jarman-Smith M, McFetridge P, Sikavitsas V. In vitro analysis of novel porous PEEK orthopedic biomaterial. Transactions of the Society for Biomaterials, 2009.
    • Keywords:
    • Porous PEEK, PEEK, biocompatibility
    • Permissions:
    • The PDF of the conference presentation is made available on with the permission of the authors.

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Introduction: Because PEEK is inert and non-porous, the material has suffered from low cell adhesion and lack of cellular ingrowth. A new porous form of the PEEK thermoplastic with approximately 25% porosity and pores ranging up to 200 microns in diameter has been produced. Researchers from the University of Oklahoma have evaluated this new material through in vitro culture with rat mesenchymal stem cells (MSCs), to assess cellular interactions and differentiation. Scanning electron microscopy (SEM) was also used to assess the morphological state of cells during osteogenic differentiation.

Methods: Constructs of non-porous PEEK were obtained from Invibio Inc. Polymer sections were cut to 7.25 mm (W) x 13.5 mm (L) x 4.25 mm (H). After ethylene oxide sterilization, polymer constructs where placed in cell culture media under vacuum to displace the air in the pores. They were then seeded with 5x105 cells/0.1 mL each. Constructs were cultured for 1, 3, 7, 14, and 21 days in osteogenic media. At each time point, seeded constructs were collected. SEM samples were rinsed, fixed, dehydrated, and sputter coated. All other scaffolds were ground, sonicated, and frozen to lyse cells before being assayed. Assays quantified DNA, alkaline phosphatase (ALP) activity, calcium deposition, and the level of osteopontin.

Results:  Quantification of cellular DNA showed that the mean cell density did not change significantly over the experimental time course. The activity of the intracellular enzyme alkaline phosphatase, an early marker of osteoblastic differentiation, rose briefly, followed by a significant reduction at three weeks. The level of osteopontin stayed approximately the same throughout the experiment. Calcium was also shown to significantly increase between days 7 and 21 of culture. SEM image analysis shows control (unseeded sections) as well as cells cultured from days 3, 7, 14, and 21 in vitro. Over time, cells are shown to become less rounded and the matrix progressively more calcified as the cells become more differentiated down the osteoblastic lineage. In addition, specific elements were imaged with SEM, showing carbon, calcium, and phosphorus. Calcium and phosphorus, the components of hydroxyapatite, were seen to increase from 7 days to 21 days. In addition, the areas rich in calcium also appear to have the most differentiated cell morphologies.

Conclusions: The cells in this study were seen to rapidly differentiate to an osteoblast-like phenotype, with a degree of cell invasion into pores, as noted through SEM imaging. As such, porous PEEK may significantly improve the bonds between the implant and native tissue, with less probability for capsule formation and stress shielding concerns. Overall, the new porous PEEK biomaterial shows promising cellular interactions that may lead to improved in vivo tissue/biomaterial integration. As such, in vivo analysis would be an important next step.